1. Field of the Invention
The invention relates to a method for transfer of a jaw model of a patient in relation to a hinge axis, a registration system for performing the method, a connection device for connecting a lower jaw adapter with a measurement carrier, as well as a bite carrier.
2. The Prior Art
Frequently, dental-technology work, such as preparation, production, and adaptation of tooth replacements, production of inlays or occlusal splints, etc., can be carried out only in part on the patient, i.e. in the patient's mouth itself, and instead must take place, at least to a significant part, in the dental technology laboratory, for example, in an articulator. In this connection, the articulator has the task of more or less precisely replicating the geometric conditions in the region of the patient's jaw, i.e. of simulating them at the work place of the dental technician.
In the sense of the quality and the required precision of dental technology work, which frequently lies in the range of hundredths of a millimeter or even less because of the great sensory sensitivity of the gnathological system in humans, it can become necessary in this connection—depending on the complexity of the work to be performed—to very precisely model the patient's chewing apparatus and its geometric characteristic values in the dental technology articulator.
These fundamental geometric characteristic values of the jaw geometry that must be transferred to the articulator include, in particular—but by no means exclusively—the spatial relative positions of the rows of teeth in the upper jaw and the lower jaw with regard to one another, as well as with regard to the patient's hinge axis, in other words the joint axis of the lower jaw with reference to the upper jaw or skull, respectively. Since these geometric characteristic values are different for every patient, the so-called average value settings of these geometric characteristic values, particularly an average setting of the hinge axis position on the articulator, can at most be used for dental technology work that sets only low precision requirements.
For more demanding dental technology work, however, it is usually absolutely necessary to reproduce the gnathological geometry of patients, and, in this connection, particularly the spatial relative position of the jaw with regard to the patient's hinge axis, with the greatest possible precision, in the articulator.
Reproduction of the geometric conditions at the jaw of a patient in an articulator usually takes place, in this connection, in that a model of a first row of teeth of the patient is mounted in an articulator, by means of corresponding transfer methods or transfer devices, with the correct position and location with reference to the hinge axis of the articulator. Subsequently, a model of the second row of teeth of the patient, in the occluded position relative to the first row of teeth, is also positioned in the articulator—this usually takes place by means of a centered registration, in other words using an impression of both rows of the patient's teeth in the occluded position, in a suitably thin impression material—and then the model of the second row of teeth, in this occluded position, is also attached to the articulator. In this manner, the relative position of the two rows of the patient's teeth with regard to one another, as well as with regard to the hinge axis of the patient, i.e. also with regard to the articulator hinge axis, is reproduced in the articulator.
In the methods and devices known from the state of the art for the transfer of jaw models of a patient, transfer of the geometric relative relationships between jaw and hinge axis that are present at the patient's skull, to the dental technology articulator, i.e. to an articulator assembly stand, generally takes place by means of a facial arc. In this connection, the facial arc serves to store the spatial relative position of a row of the patient's teeth, with regard to the hinge axis of the patient, in most cases in mechanical manner, i.e. to code it by means of corresponding adjustment of the facial arc, in such a manner that this spatial relative position between the row of teeth and the hinge axis of the patient can also be reproduced later, outside of the patient, particularly in the dental technology laboratory, i.e. on the articulator.
For this purpose, in the state of the art, the spatial relative position between the row of teeth of the upper jaw, on the one hand, and certain fixed points on the patient's skull, on the other hand, is generally recorded by means of corresponding adjustment of the facial arc, i.e. therefore coded in the facial arc. In this connection, the so-called arbitrary facial arc transfer known from the state of the art, on the one hand, usually makes use of an empirically determined relationship between the typical location of the hinge axis relative to the patient's porion—in other words relative to the highest point of the external auditory meatus—on the human skull.
In this known arbitrary facial arc transfer, it is therefore not the actual hinge axis that is recorded on the patient's skull and coded by means of the facial arc, for transfer to the articulator, but rather—for example by means of corresponding ear olives disposed on the facial arc that are introduced into the external auditory meatus of the patient—a conclusion is drawn from the position of the porion to the location of the patient's hinge axis, merely on the basis of statistical average values.
The arbitrary facial arc transfer can therefore only guarantee an average reproduction, but by no means a precise reproduction of the geometrical conditions of the gnathological system of a patient in the articulator, and is therefore also suited only for use in less demanding work in the dental technology laboratory, in which the main point of importance is reproduction of the correct occlusion between upper jaw and lower jaw, which is undertaken by means of a centered registration.
More demanding restoration work in the articulator, however, frequently requires not only an average transfer, but rather an individual and precise transfer of the hinge axis location relative to the rows of teeth of the patient's jaw. In the state of the art, the determination and transfer of the actual hinge axis location required for this generally take place on the basis of a kinematic determination of the patient's hinge axis. This kinematic hinge axis determination can be carried out electronically, for example using a lower jaw measurement arc—or by means of mechanical pin recording. In this connection, the actual patient hinge axis that is determined can subsequently be coded onto a so-called terminal facial arc, on which, in contrast to the arbitrary facial arc, the location of the hinge axis can be adjusted and thus individually transferred to the articulator.
However, in the state of the art, it is necessary, even in the case of a geometry transfer by means of kinematic axis determination and terminal facial arc, to first record the kinematically determined actual hinge axis location by means of corresponding measurement markings, mostly on the patient's skin. Subsequent to this, the apparatus used for axis localization is removed from the patient's head, the terminal facial arc is coupled with the row of teeth of the upper jaw, and the arc is adjusted to the previously applied joint axis measurement markings. However, since the patient's skin is easily movable relative to the patient's skull—and thus the measurement markings placed on the skin are easily movable with reference to the hinge axis location—this can already induce not insignificant transfer errors when using a terminal facial arc.
In every case, however—even independent of whether or not imprecisions are induced by means of easily displaceable measurement markings placed on the patient's skin—simply the double transfer process of the hinge axis measurement values first from the measurement arc to the measurement markings, and then the manual recording of the measurement markings by means of a facial arc, brings not insignificant error sources with it.
Only subsequent to the corresponding adjustment of the terminal facial arc—particularly using the markings relating to the hinge axis location on the patient's head—can the facial arc then be removed from the patient's head, and the gnathological geometry of the patient can be transferred to an articulator or an articulator assembly stand, by means of the spatial relative relationship between the row of teeth of the upper jaw and the kinematically determined condylar axis now stored in the facial arc.
In the end result, it must be stated, with regard to the known methods and devices for transfer of jaw models to an articulator, that the methods and devices known from the state of the art—particularly due to the need to record the skull geometry by means of a facial arc and to transfer it to the articulator—are extremely complicated, on the one hand, and are subject to error, on the other hand.
Even passing on the complete facial arc—or at least a bite fork with upper jaw teeth impression and a sensitive coupling mechanism disposed on the bite fork, adjusted to the jaw geometry of the patient—which is absolutely necessary for the purpose of geometry transfer in the state of the art, to the dental technology laboratory is complicated and tends to be expensive because of the need to keep these components on hand in multiple numbers for different patients. Last but not least, there is the additional risk in connection with passing the facial arc or the adjusted coupling mechanism on to the dental technology laboratory, particularly when shipping it, that the precise adjustment that has been made is unintentionally changed as the result of the effect of external forces, and this unavoidably leads to the result of expensive scrap in the dental technology laboratory.